The invention relates to electrical machines. More specifically, the invention relates to a drive for a brushless dc motor.
A brushless dc motor typically utilizes rotor position sensors for providing information regarding the position of the motor's rotor with respect to the motor's stator windings. The positional information allows for proper commutation and control of the stator windings. Rotor position sensors such as Hall effect devices are typically mounted in the stator, proximate the motor windings. The rotor position sensors provide intelligence upon rotor position.
Rotor position sensors can be unreliable due to mechanical alignment problems (e.g., problems caused by bearings) and temperature incompatibility problems between the motor windings and electronic components such as the Hall effect devices. Moreover, the rotor position sensors can be difficult to mount to the motor during motor assembly, especially for multi-pole motors. In multi-pole motors, the electrical misalignment angle is equivalent to the angular mechanical misalignment angle multiplied by the number of pairs of poles.